Scroll type fluid machines have been well known in the prior art. For example, Japanese Patent Kokai number (1994)330864 discloses a compressor composed of a scroll type fluid machine.
An arrangement of a typical scroll type fluid machine will be described below. This type of fluid machine includes a stationary scroll and a movable scroll. The stationary and movable scrolls include respective tabular flat plate portions and spiral wraps. In both the scrolls, the wraps are vertically arranged on front surface sides of the flat plate portions. Additionally, in both the scrolls the wraps are formed integrally with the flat plate portions, respectively. The stationary and movable scrolls are disposed in such an orientation that they face each other, and their respective wraps are matingly engaged with each other. The wraps, which are being engaged with each other, are sandwiched between the flat plate portions. In this state, a fluid chamber is comparted by the wraps and the flat plate portions.
The stationary scroll is secured firmly to a housing of the fluid machine. On the other hand, the movable scroll is placed in the housing through an Oldham ring. This Oldham ring constitutes a rotation preventing mechanism for preventing rotation of the movable scroll. Additionally, in the movable scroll a bearing is formed on a back surface side of the flat plate portion, and an eccentric portion of a rotary shaft engages with the bearing. The movable scroll orbits but does not rotate.
When such a scroll type fluid machine is used as a refrigerant compressor, a gas refrigerant is drawn to areas near the outer peripheral side ends of the wraps. The gas refrigerant is trapped in the inside of the fluid chamber. When the movable scroll is driven through the rotary shaft, the volume of the fluid chamber gradually decreases, and the gas refrigerant in the inside of the fluid chamber is compressed. When the fluid chamber reaches near the inner peripheral side ends of the wraps, the compressed gas refrigerant is discharged through discharge ports opening to the flat plate portions.
Problems that Invention Intends to Solve
In a scroll type fluid machine a movable scroll executes an orbital motion with its wrap in mating engagement with a stationary scroll wrap. During that period, wrap side surfaces of both the scrolls come into sliding contact with each other and, furthermore, wrap tips and flat plate portions of both the scrolls come into sliding contact with each other. If there is created an excessive gap between the wraps which are sliding against each other or between the wrap tip and the flat plate portion which are sliding against each other, this will cause leakage of fluid from the fluid chamber. As a result, the efficiency of the fluid machine will drop. Consequently, in order to avoid the drop in fluid machine efficiency, it is required that surfaces which are brought into sliding contact with each other (i.e., sliding surfaces) be finished with a high degree of accuracy.
However, the problem with conventional scroll type fluid machines is that it is difficult to provide highly accurately machined sliding surfaces to the wrap tip and the flat plate portion. This problem will be described below.
For example, the movable side wrap tip of the movable scroll slides against the stationary side flat plate portion of the stationary scroll. On the other hand, as has been described above, in each scroll the wrap is formed integrally with the flat plate portion. Consequently, the sliding surface of the stationary side flat plate portion with respect to the movable side wrap tip lies at the bottom of the stationary side wrap.
Accordingly, high accuracy machining of the sliding surface of the flat plate portion with respect to the wrap tip is difficult to carry out. In other words, it is difficult to reduce the surface roughness of the sliding surface and it is also difficult to improve the flatness of the sliding surface. Consequently, in conventional scroll type fluid machines it is impossible to effectively control leakage of fluid through a gap between the wrap tip and the flat plate portion. Due to this, it is difficult to achieve improvements in efficiency.
Bearing in mind the above-described problems, the present invention was made. Accordingly, an object of the present invention is to make it possible to machine wrap tip and flat plate portion sliding surfaces with ease and with high accuracy, for improving the efficiency of fluid machinery.